Exception Clause - Advanced Usage

// default should errors go to mock:error
errorHandler(deadLetterChannel("mock:error").redeliveryDelay(0));

// if a MyTechnicalException is thrown we will not try to
// redeliver and we mark it as handled
// so the caller does not get a failure
// since we have no to then the exchange will continue to be
// routed to the normal error handler
// destination that is mock:error as defined above
onException(MyTechnicalException.class).maximumRedeliveries(0).handled(true);

// if a MyFunctionalException is thrown we do not want Camel to
// redelivery but handle it our self using
// our bean myOwnHandler, then the exchange is not routed to the
// default error (mock:error)
onException(MyFunctionalException.class).maximumRedeliveries(0).handled(true).to("bean:myOwnHandler");

// here we route message to our service bean
from("direct:start").choice().when().xpath("//type = 'myType'").to("bean:myServiceBean").end().to("mock:result");

// default should errors go to mock:error
errorHandler(deadLetterChannel("mock:error"));

// here we start the routing with the consumer
from("direct:start")

    // if a MyTechnicalException is thrown we will not try to
    // redeliver and we mark it as handled
    // so the caller does not get a failure
    // since we have no to then the exchange will continue to be
    // routed to the normal error handler
    // destination that is mock:error as defined above
    // we MUST use .end() to indicate that this sub block is
    // ended
    .onException(MyTechnicalException.class).maximumRedeliveries(0).handled(true).end()

    // if a MyFunctionalException is thrown we do not want Camel
    // to redelivery but handle it our self using
    // our bean myOwnHandler, then the exchange is not routed to
    // the default error (mock:error)
    // we MUST use .end() to indicate that this sub block is
    // ended
    .onException(MyFunctionalException.class).maximumRedeliveries(0).handled(true).to("bean:myOwnHandler").end()

    // here we have the regular routing
    .choice().when().xpath("//type = 'myType'").to("bean:myServiceBean").end().to("mock:result");

// global error handler
// as its based on a unit test we do not have any delays between
// and do not log the stack trace
errorHandler(deadLetterChannel("mock:error").redeliveryDelay(0).logStackTrace(false));

// shared for both routes
onException(MyTechnicalException.class).handled(true).maximumRedeliveries(2).to("mock:tech.error");

from("direct:start")
    // route specific on exception for MyFunctionalException
    // we MUST use .end() to indicate that this sub block is
    // ended
    .onException(MyFunctionalException.class).maximumRedeliveries(0).end().to("bean:myServiceBean").to("mock:result");

from("direct:start2")
    // route specific on exception for MyFunctionalException
    // that is different than the previous route
    // here we marked it as handled and send it to a different
    // destination mock:handled
    // we MUST use .end() to indicate that this sub block is
    // ended
    .onException(MyFunctionalException.class).handled(true).maximumRedeliveries(0).to("mock:handled").end().to("bean:myServiceBean").to("mock:result");

from("direct:start3")
    // route specific error handler that is different than the
    // global error handler
    // here we do not redeliver and send errors to mock:error3
    // instead of the global endpoint
    .errorHandler(deadLetterChannel("mock:error3").maximumRedeliveries(0))

    // route specific on exception to mark MyFunctionalException
    // as being handled
    .onException(MyFunctionalException.class).handled(true).end()
    // however we want the IO exceptions to redeliver at most 3
    // times
    .onException(IOException.class).maximumRedeliveries(3).end().to("bean:myServiceBean").to("mock:result");

// This is our processor that is executed before every redelivery attempt
// here we can do what we want in the java code, such as altering the
// message
public static class MyRedeliverProcessor implements Processor {

    @Override
    public void process(Exchange exchange) throws Exception {
        // the message is being redelivered so we can alter it

        // we just append the redelivery counter to the body
        // you can of course do all kind of stuff instead
        String body = exchange.getIn().getBody(String.class);
        int count = exchange.getIn().getHeader("CamelRedeliveryCounter", Integer.class);

        exchange.getIn().setBody(body + count);
    }
}

// we want to use a predicate for retries so we can determine in
// our bean when retry should stop, notice it will overrule the global
// error handler where we defined at most 1 redelivery attempt. Here we will
// continue until the predicate returns false
onException(MyFunctionalException.class).retryWhile(method("myRetryHandler")).handled(true).transform().constant("Sorry");

public class MyRetryBean {

    // using bean binding we can bind the information from the exchange to
    // the types we have in our method signature
    public boolean retry(@Header(Exchange.REDELIVERY_COUNTER) Integer counter) {
        // NOTE: counter is the redelivery attempt, will start from 1
        // we can of course do what ever we want to determine the result but
        // this is a unit test so we end after 3 attempts
        return counter < 3;
    }
}

// configure the error handler to use my policy instead of the default from Camel
errorHandler(deadLetterChannel("mock:error").exceptionPolicyStrategy(new MyPolicy()));

public static class MyPolicy implements ExceptionPolicyStrategy {

    @Override
    public ExceptionPolicyKey getExceptionPolicy(Set<ExceptionPolicyKey> exceptionPolicies, Exchange exchange, Throwable exception) {
        // This is just an example that always forces the exception type configured
        // with MyPolicyException to win.
        return new ExceptionPolicyKey(null, MyPolicyException.class, null);
    }
}